U.S. patent application number 11/474339 was filed with the patent office on 2007-12-27 for wiring board with built-in capacitor.
This patent application is currently assigned to IBIDEN CO., LTD.. Invention is credited to Hironori Tanaka.
Application Number | 20070297157 11/474339 |
Document ID | / |
Family ID | 38474398 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070297157 |
Kind Code |
A1 |
Tanaka; Hironori |
December 27, 2007 |
WIRING BOARD WITH BUILT-IN CAPACITOR
Abstract
The invention provides a wiring board with built-in capacitors,
that has a multilayer wiring structure and capable of mounting an
IC chip thereon. The wiring board with built-in capacitors
includes: a first capacitor that is built into the multilayer
wiring structure and formed so that an overlapping area between a
first lower electrode and a first upper electrode provided on
respective surfaces of a first dielectric layer is a predetermined
area; and a second capacitor that is built into the multilayer
wiring structure along the same plane as the first dielectric layer
and formed so that an overlapping area between a second lower
electrode and a second upper electrode provided on respective
surfaces of a second dielectric layer with the same thickness as
the first dielectric layer is different from the predetermined
area. The wiring board further includes: a line that electrically
connects either one of a power pad for supplying power to the IC
chip and a ground pad for grounding the IC chip to either one of
the first lower electrode and the second lower electrode; and a
line that electrically connects the other of the power pad and the
ground pad to the other of the first upper electrode and the second
upper electrode.
Inventors: |
Tanaka; Hironori; (Ibi-gun,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
IBIDEN CO., LTD.
Ogaki-shi
JP
|
Family ID: |
38474398 |
Appl. No.: |
11/474339 |
Filed: |
June 26, 2006 |
Current U.S.
Class: |
361/766 ;
257/E23.062; 257/E23.079 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 2924/0002 20130101; H05K 3/4602 20130101; H01L 23/50 20130101;
H01L 2924/3011 20130101; H05K 1/112 20130101; H05K 2201/09509
20130101; H05K 2201/09672 20130101; H05K 2201/10674 20130101; H01L
23/49822 20130101; H05K 2201/09309 20130101; Y10T 29/4913 20150115;
H05K 1/162 20130101; H05K 3/4641 20130101; H05K 2201/09718
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
361/766 |
International
Class: |
H05K 1/16 20060101
H05K001/16 |
Claims
1. A wiring board with built-in capacitors, that has a multilayer
wiring structure and capable of mounting an IC chip thereon, said
wiring board with built-in capacitors comprising: a first capacitor
that is built into the multilayer wiring structure and formed so
that an overlapping area between a first lower electrode and a
first upper electrode provided on respective surfaces of a first
dielectric layer is a predetermined area; a second capacitor that
is built into the multilayer wiring structure along the same plane
as the first dielectric layer and formed so that an overlapping
area between a second lower electrode and a second upper electrode
provided on respective surfaces of a second dielectric layer with
the same thickness as the first dielectric layer is different from
the predetermined area; a line that electrically connects either
one of a power pad for supplying power to the IC chip and a ground
pad for grounding the IC chip to either one of the first lower
electrode and the second lower electrode; and a line that
electrically connects the other of the power pad and the ground pad
to the other of the first upper electrode and the second upper
electrode.
2. The wiring board with built-in capacitors according to claim 1,
wherein the first dielectric layer and the second dielectric layer
are integrated as a single dielectric layer.
3. The wiring board with built-in capacitors according to claim 1,
wherein the first dielectric layer and the second dielectric layer
are sintered ceramic bodies.
4. The wiring board with built-in capacitors according to claim 1,
wherein the first lower electrode and the second lower electrode
are separated, the first upper electrode and the second upper
electrode are separated, and the overlapping area between the first
lower electrode and the first upper electrode is different from the
overlapping area between the second lower electrode and the second
upper electrode.
5. The wiring board with built-in capacitors according to claim 1,
wherein the first lower electrode and the second lower electrode
are integrated as a single electrode plate, and the overlapping
area between the first upper electrode and the single electrode
plate is different from the overlapping area between the second
upper electrode and the single electrode plate.
6. The wiring board with built-in capacitors according to claim 1,
wherein the first upper electrode and the second upper electrode
are integrated as a single electrode plate, and the overlapping
area between the first lower electrode and the single electrode
plate is different from the overlapping area between the second
lower electrode and the single electrode plate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention related to a wiring board with
built-in capacitors. Specifically, the invention relates to a
wiring board with built-in capacitors, which has a multilayer
wiring structure and capable of mounting an IC chip thereon.
[0003] 2. Description of the Prior Art
[0004] In a proposed wiring board on which an IC chip can be
mounted, a thin film capacitor is connected between a power line
and a ground line of the IC chip to realize decoupling and restrain
instantaneous lowering of the potential of the power line due to
switching noise resulting from high-speed ON/OFF of the mounted IC
chip. For example, in a substrate disclosed in Patent Document 1
(JP 2005-191266 A), a plurality of capacitors which are differing
in dielectric film thickness are connected in parallel between a
power line and a ground line of an IC chip to reduce the impedance
across a wider range of frequencies in comparison to a substrate
using a single capacitor.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a wiring board with
built-in capacitors, that has a multilayer wiring structure and
capable of mounting an IC chip thereon. The wiring board with
built-in capacitors of the invention includes: a first capacitor
that is built into the multilayer wiring structure and formed so
that an overlapping area between a first lower electrode and a
first upper electrode provided on respective surfaces of a first
dielectric layer is a predetermined area; a second capacitor that
is built into the multilayer wiring structure along the same plane
as the first dielectric layer and formed so that an overlapping
area between a second lower electrode and a second upper electrode
provided on respective surfaces of a second dielectric layer with
the same thickness as the first dielectric layer is different from
the predetermined area; a line that electrically connects either
one of a power pad for supplying power to the IC chip and a ground
pad for grounding the IC chip to either one of the first lower
electrode and the second lower electrode; and a line that
electrically connects the other of the power pad and the ground pad
to the other of the first upper electrode and the second upper
electrode.
[0006] In this wiring board with built-in capacitors, because the
overlapping area between the upper electrode and the lower
electrode of the first capacitor differs from the overlapping area
(crossover) between the upper electrode and the lower electrode of
the second capacitor, the capacitance of the first capacitor
differs from the capacitance of the second capacitor. As a result,
a state that is the same as connecting a plurality of decoupling
capacitors of different capacitances in parallel between the line
connected to the power pad and the line connected to the ground pad
is realized. Here, although with each of the first and second
capacitors, the impedance takes on a minimum value at a
corresponding resonance frequency, because the capacitors differ in
capacitance, the respective resonant frequencies differ and the
impedance is restrained to a low value across a wide frequency
range. In addition, because the first and second capacitors are the
same in the thickness of the dielectric layer and are disposed in
parallel, the respective dielectric layers can be formed more
readily in the process of forming the multilayer wiring structure
and the first and second capacitors can thus be formed readily in
comparison to a case of using dielectric layers that differ in
thickness according to each capacitor.
[0007] Here, description regards two capacitors that are
respectively defined as the first capacitor and the second
capacitor in the wiring board of the invention. However, it is
obvious that a wiring board with not less than three capacitors is
within the scope of the claims of the present invention, as long as
some capacitor built into the wiring board meets the requirement of
the first capacitor of the invention and other capacitor built into
the wiring board meets the requirement of the second capacitor of
the invention. In the specification, "same" means to be the same in
consideration of errors that may arise in design or in manufacture
and applies to cases of complete sameness as well as cases of
substantial sameness. Also, in the present specification, the
overlapping area between the upper electrode and the lower
electrode of each capacitor is preferably set in a range from 150
.mu.m square to 10 mm square. In this case, the different
overlapping areas take on different values between an area of 150
.mu.m square and an area of 10 mm square.
[0008] In the wiring board with built-in capacitors of the
invention, the first dielectric layer and the second dielectric
layer may be integrated as a single dielectric layer. Because a
single dielectric layer can be used without partitioning,
troublesome processes are eliminated and the manufacturing process
is simplified in comparison to the case where the first dielectric
layer and the second dielectric layer are separated.
[0009] In the wiring board with built-in capacitors of the
invention, the first dielectric layer and the second dielectric
layer may be sintered ceramic bodies. The dielectric constants of
the dielectric layers can be adequately high, the first and second
capacitors can be high in capacitance and can be functioned as
charge supply sources for accommodating instantaneous lowering of
power supply voltage. The sintered ceramic body is not restricted
in particular, but may be a body formed by sintering a raw material
containing one or two or more types of metal oxide selected from
the group consisting of barium titanate (BaTiO.sub.3), strontium
titanate (SrTiO.sub.3), tantalum oxide (TaO.sub.3,
Ta.sub.2O.sub.5), lead zirconate titanate (PZT), lead lanthanum
zirconate titanate (PLZT), lead niobium zirconate titanate (PNZT),
lead calcium zirconate titanate (PCZT), and lead strontium
zirconate titanate (PSZT).
[0010] In one preferable structure of the wiring board with
built-in capacitors of the invention, the first lower electrode and
the second lower electrode are separated, the first upper electrode
and the second upper electrode are separated, and the overlapping
area between the first lower electrode and the first upper
electrode is different from the overlapping area between the second
lower electrode and the second upper electrode. In another
preferable structure of the wiring board with built-in capacitors
of the invention, the first lower electrode and the second lower
electrode are integrated as a single electrode plate, and the
overlapping area between the first upper electrode and the single
electrode plate is different from the overlapping area between the
second upper electrode and the single electrode plate. In still
another preferable structure of the wiring board with built-in
capacitors of the invention, the first upper electrode and the
second upper electrode are integrated as a single electrode plate,
and the overlapping area between the first lower electrode and the
single electrode plate is different from the overlapping area
between the second lower electrode and the single electrode
plate.
[0011] Although in the present specification, descriptions using
the terms, "upper," "lower," "right," and "left" shall be given,
these terms are merely used for clarifying positional relationships
of components. Thus, for example, an "upper" and "lower"
relationship may be inverted or a "right" and "left" relationship
may be inverted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a plan view of a multilayer printed wiring board
10;
[0013] FIG. 2 is a schematic sectional view of the multilayer
printed wiring board 10;
[0014] FIG. 3 is a sectional view of principal portions of the
multilayer printed wiring board 10;
[0015] FIG. 4 is a perspective view of first and second capacitors
140 and 240 inside the multilayer printed wiring board 10;
[0016] FIG. 5 is a graph showing a relationship between frequency
and impedance of the first and second capacitors 140 and 240;
[0017] FIG. 6 show explanatory drawings of a process of
manufacturing the multilayer printed wiring board 10, where FIG. 6A
being a perspective view of a high dielectric constant sheet 340,
FIG. 6B being a perspective view of a state after processing a
lower electrode 41, and FIG. 6C being a sectional view taken on A-A
of FIG. 6B;
[0018] FIG. 7 show explanatory drawings of the process of
manufacturing the multilayer printed wiring board 10;
[0019] FIG. 8 show explanatory drawings of the process of
manufacturing the multilayer printed wiring board 10;
[0020] FIG. 9 show explanatory drawings of the process of
manufacturing the multilayer printed wiring board 10;
[0021] FIG. 10 is a perspective view of first and second capacitors
140 and 240 of another embodiment;
[0022] FIG. 11 is a perspective view of first and second capacitors
140 and 240 of another embodiment; and
[0023] FIG. 12 is a graph showing a relationship between frequency
and impedance of a capacitor of another embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Embodiments of the present invention shall now be described
with reference to the drawings. FIG. 1 is a plan view of a
multilayer printed wiring board 10 that is a first embodiment
according to the present invention, FIG. 2 is a schematic sectional
view of the multilayer printed wiring board 10, FIG. 3 is a
sectional view of principal portions of the multilayer printed
wiring board 10, and FIG. 4 is a perspective view of first and
second capacitors 140 and 240 inside the multilayer printed wiring
board 10.
[0025] The multilayer printed wiring board 10 according to the
present embodiment is an example of a wiring board with built-in
capacitors according to the present invention. As shown in FIG. 1
and FIG. 2, the multilayer printed wiring board has, on the surface
of the board, a mounting portion 60 for mounting an IC chip 70. The
mounting portion 60 includes a ground pad 61 connected to a ground
line GL that grounds the IC chip 70, a power pad 62 connected to a
power line PL that supplies a power supply potential to the IC chip
70, and a signal pad 63 connected to a signal line SL that inputs
and outputs signals into and from the IC chip 70. In the present
embodiment, ground pads 61 and power pads 62 are arrayed in lattice
or staggered form at a central portion of the mounting portion 60,
and signal pads 63 are arrayed in lattice form, staggered form, or
randomly to surround the arrayed ground pads and power pads. The
ground pads 61 are connected, via the ground lines GL that are
formed in the interior of the multilayer printed wiring board 10
independently of the power lines PL and the signal lines SL, to
external ground terminals 66 formed on the surface at the opposite
side of mounting portion 60, and power pads 62 are connected, via
the power lines PL that are formed in the interior of the
multilayer printed wiring board 10 independently of the ground
lines GL and the signal lines SL, to external power terminals 67
formed on the surface at the opposite side of mounting portion 60.
The power lines PL are connected to upper electrodes 142 and 242 of
first and second capacitors 140 and 240, and the ground lines GL
are connected to lower electrodes 141 and 241 of the first and
second capacitors 140 and 240. The signal pads 63 are connected,
via the signal lines SL that are formed in the interior of the
multilayer printed wiring board 10 independently of the power lines
PL and the ground lines GL, to external signal terminals 68 formed
on the surface at the opposite side of the mounting portion 60. The
total number of pads of mounting portion 60 is approximately 1000
to 30000.
[0026] The structure of the multilayer printed wiring board 10
shall now be described in more detail with reference to FIG. 3. The
multilayer printed wiring board 10 includes a core substrate 20,
and the above-mentioned first and second capacitors 140 and 240
that are formed, across an insulating layer 26, on an upper side of
core substrate 20, a build-up portion 30 formed on upper sides of
first and second capacitors 140 and 240. The multilayer printed
wiring board 10 further includes the above-mentioned mounting
portion 60 formed on an uppermost layer of build-up layer 30. The
respective pads of mounting portion 60 are electrically connected
to internal build-up portion conductor layers (BU conductor layers)
32 that are wiring patterns laminated inside the build-up portion
30.
[0027] The core substrate 20 includes conductor layers 22 formed of
copper on both top and rear surfaces of a main core substrate body
21 that is formed of BT (bismaleimide triazine) resin or glass
epoxy substrate, etc., and through hole conductors 24 provided on
inner surfaces of through holes which pass through from the top to
rear of the main core substrate body 21. The conductor layers 22 on
the respective surfaces are electrically connected via the through
hole conductors 24.
[0028] As shown in FIG. 3 and FIG. 4, the first capacitor 140
includes a dielectric layer 43 that is formed by sintering a
ceramic-based high dielectric constant material at high
temperature, and the first lower electrode 141 and the first upper
electrode 142 that sandwich the dielectric layer 43. The first
lower electrode 141 is a nickel electrode that is formed on a lower
surface of the dielectric layer 43 and is electrically connected to
the ground pad 61 of the mounting portion 60, and the first upper
electrode 142 is a copper electrode that is formed on an upper
surface of the dielectric layer 43 and is electrically connected to
the power pad 62 of the mounting portion 60. The first lower
electrode 141 and first upper electrode 142 are thus connected
respectively to a ground terminal and a power terminal of the IC
chip 70 that is mounted onto the mounting portion 60. The first
lower electrode 141 is a solid pattern with a larger area than the
second lower electrode 241, and has a circular hole 141a, through
which a first upper via hole conductor 148 electrically connecting
a power line conductor layer 22P of the conductor layers 22 of the
core substrate 20 and the first upper electrode 142 passes in a
non-contacting state. Meanwhile, the first upper electrode 142 is
formed on a position of the upper surface of dielectric layer 43
that opposes the first lower electrode layer 141. The first upper
electrode 142 is a solid pattern that is substantially equivalent
in shape and area to the first lower electrode 141, and has a
clearance 142a, through which a first lower via hole conductor 145
electrically connecting a ground line conductor layer 22G of the
conductor layers 22 of the core substrate 20 and the first lower
electrode 142 passes in a non-contacting state. The dielectric
layer 43 is made of a single dielectric film and is formed by
forming a high dielectric constant material, containing one or more
types of metal oxide, selected from the group consisting of
BaTiO.sub.3, SrTiO.sub.3, TaO.sub.3, Ta.sub.2O.sub.5, PZT, PLZT,
PNZT, PCZT, and PSZT, into a thin film of 0.1 to 10 .mu.m and
thereafter sintering the film into a ceramic material.
[0029] As shown in FIG. 3 and FIG. 4, the second capacitor 140
includes the dielectric layer 43, and second lower electrode 241
and second upper electrode 242 that sandwich the dielectric layer
43. In the second capacitor 240, the second lower electrode 241 is
a nickel electrode that is formed on the lower surface of the
dielectric layer 43 and is electrically connected to the ground pad
61 of the mounting portion 60, and the second upper electrode 242
is a copper electrode that is formed on the upper surface of the
dielectric layer 43 and is electrically connected to the power pad
62 of the mounting portion 60. The second lower electrode 241 and
second upper electrode 242 are thus connected respectively to the
ground terminal and the power terminal of the IC chip 70 that is
mounted onto the mounting portion 60. The second lower electrode
241 is a solid pattern with a smaller area than the first lower
electrode 141 and has a circular hole 241a, through which a second
upper via hole conductor 248 electrically connecting a power line
conductor layer 22P of conductor layers 22 of the core substrate 20
and the second upper electrode 242 passes in a non-contacting
state. Meanwhile, the second upper electrode 242 is formed on a
position of the upper surface of the dielectric layer 43 that
opposes the second lower electrode layer 241. The second upper
electrode 242 is a solid pattern that is substantially equivalent
in shape and area to the second lower electrode 241, and has a
clearance 242a, through which a second lower via hole conductor 245
electrically connecting a ground line conductor layer 22G of the
conductor layers 22 of the core substrate 20 and the second lower
electrode 242 passes in a non-contacting state.
[0030] Here, the first and second lower electrodes 141 and 241 are
electrodes having substantially the same thickness and are both
formed on the upper surface of the insulating layer 26, and the
first and second upper electrodes 142 and 242 are electrodes having
substantially the same thickness and are both formed on the upper
surface of the dielectric layer 43. The capacitance C1 of the first
capacitor 140 satisfies the expression C1=.epsilon.S1/d, where S1
represents the area of the first lower electrode 141 and the first
upper electrode 142, d represents the thickness of the dielectric
layer 43, and E represents the dielectric constant of the
dielectric layer 43. In addition, the capacitance C2 of the second
capacitor 240 satisfies the expression C2=.epsilon.S2/d, where S2
represents the area of the second lower electrode 241 and second
upper electrode 242. Because the area S1 is greater than the area
S2, the capacitance C1 of the first capacitor 140 is greater than
the capacitance C2 of the second capacitor 240. And, because an
equivalent circuit of each of the first and second capacitors 140
and 240 is a parallel LC circuit, the relationship between
frequency and impedance the impedance gets to a minimum value at a
resonant frequency. Because the resonant frequency is proportional
to the reciprocal of the square root of the capacitance, the value
of resonant frequency of the first capacitor 140 with the higher
capacitance is smaller than that of the second capacitor 240 with
the lower capacitance. The relationships between the impedance and
the frequency in this case are shown in FIG. 5. In FIG. 5, both the
abscissa and the ordinate are of logarithmic scale.
[0031] The first and second lower electrodes 141 and 241 and the
first and second upper electrodes 142 and 242 may have through
holes, through which the respective signal lines pass from top to
bottom in a non-contacting state. However, it is more preferable
that the respective signal lines are formed at outer sides of the
first and second lower electrodes 141 and 241 and the first and
second upper electrodes 142 and 242 as shown in FIG. 2.
[0032] The buildup portion 30 is lamination of buildup insulating
layers (BU insulating layers) 36 and BU conductor layers 32
alternately on the upper side of first and second capacitors 140
and 240. The BU conductor layers 32 are electrically connected to
each other across the BU insulating layer 36, and are further
electrically connected to the first and second capacitors 140 and
240, by means of BU via hole conductors 34. In consideration of
making buildup portion 30 have a fine structure, the thickness of
each BU conductor layer 32 is thinner than the thickness of each of
the first and second lower electrodes 141 and 241. The mounting
portion 60 is formed on the topmost layer of the buildup portion
30. The buildup portion 30 of such structure is formed by any known
subtractive method or additive method (including a semi-additive
method and a full additive method), and may be formed for example
as follows. First, resin sheets that are to become BU insulating
layers 36 (with a Young's modulus at room temperature of, for
example, 2 to 7 GPa) are adhered onto the top and rear surfaces of
the core substrate 20. Each of these resin sheets is formed of a
modified epoxy based resin sheet, a polyphenylene ether based resin
sheet, a polyimide based resin sheet, or a cyanoester based resin
sheet, etc., and the thickness thereof is approximately 20 to 80
.mu.m. The resin sheet may have silica, alumina, zirconia, or other
inorganic component dispersed therein. Through holes are then
formed in the adhered resin sheets using a carbon dioxide gas
laser, UV laser, YAG laser, or excimer laser, etc., and electroless
copper plating is applied to the surfaces of the resin sheets and
the interiors of the through holes to form conductor layers. Then,
plating resists are formed on the conductor layers, electroless
copper plating are applied onto portions at which the plating
resists are not formed, and thereafter the electroless copper
plating below the resists are removed by an etching solution, to
obtain BU conductor layers 32. The conductor layers of the
interiors of the through holes become the BU via hole conductors
34. The buildup portion 30 is formed by repeating this procedure.
In the present embodiment, the first and second lower electrodes
141 and 241 of the first and second capacitors 140 and 240 are
formed to be thicker than each of the BU conductor layers 32.
[0033] An example of use of the multilayer printed wiring board 10
arranged as described above shall now be described. First, an IC
chip 70, having a plurality of solder bumps disposed on a rear
surface, is set on the mounting portion 60. In this process, the
ground terminals, the power terminals, the signal terminals of IC
chip 70 are respectively contacted with the ground pads 61, the
power pads 62, and the signal pads 63 of the mounting portion 60.
The respective terminals are then bonded by reflow soldering.
Thereafter, the multilayer printed wiring board 10 is bonded to a
mother board or other printed wiring board. Here, solder bumps are
formed in advance on the pads formed on the rear surface of the
multilayer printed wiring board 10 and are bonded by reflow while
being contacted to the corresponding pads on the other printed
wiring board. Because the first and second capacitors 140 and 240
built in the multilayer printed wiring board 10 have dielectric
layers 43 formed of ceramic material of high dielectric constant
and provide a wider low impedance range in comparison to a case
where just a single capacitor is incorporated, an adequate
decoupling effect can be exhibited so that transistors of the IC
chip 70 (IC) mounted on the mounting portion 60 are not likely to
be subject to power shortage, and erroneous operation due to high
frequency noise can be prevented as well. If necessary, a chip
capacitor of high capacitance may be mounted on a periphery of the
mounting portion 60 of the multilayer printed wiring board 10 and
be connected in parallel to the first and second capacitors 140 and
240. The power supplying ability can thus be improved further more
readily. When a plurality of chip capacitors are to be mounted, the
low impedance range can be widened more readily by differing the
capacitances of the respective chip capacitors.
[0034] A procedure of manufacturing the multilayer printed wiring
board 10 according to the present embodiment shall now be described
with reference to FIG. 6 to FIG. 9. First, a high dielectric
constant sheet 340 (see FIG. 6A), which includes a dielectric layer
43, a lower electrode 41 formed of nickel and covering the entire
lower surface of the dielectric layer 43, and an upper electrode 42
formed of copper and covering the entire upper surface of
dielectric layer 43, is prepared by the following procedure.
(1) Barium diethoxide and titanium bi-tetraisopropoxide, each of
which is weighed out to realize a concentration of 1.0 mole/liter,
are dissolved in a mixed solvent of dehydrated methanol and
2-methoxyethanol (volume ratio: 3:2), and the solution is stirred
for three days under a nitrogen atmosphere at room temperature to
prepare a barium and titanium alkoxide precursor composition
solution. This precursor composition solution is then stirred while
being maintained at 0.degree. C., and water, which has been
decarbonated in advance, is sprayed on at a rate of 0.5
microliters/minute in a nitrogen gas flow to perform
hydrolysis.
(2) The sol-gel solution thus prepared is passed through a 0.2
micron filter to filter out precipitates, etc.
[0035] (3) The filtrate prepared in (2) above is spin coated at
1500 rpm for 1 minute onto lower electrode 41 formed of nickel and
having a thickness of 14 .mu.m, and the substrate resulting from
the spin coating of the solution is dried by placing for 3 minutes
on a hot plate maintained at 150.degree. C. Thereafter, the
substrate is inserted in an electric oven maintained at 850.degree.
C. and sintered for 15 minutes. Here, the viscosity of the sol-gel
solution is adjusted so that the thickness of the film obtained by
the first spin coating, drying, and sintering is 0.03 .mu.m.
Besides nickel, lower electrode 41 may be formed of copper,
platinum, gold, or silver, etc.
(4) A series of the spin coating, drying, and sintering is repeated
25 times to obtain a dielectric layer 43 having a thickness of 0.75
.mu.m.
[0036] (5) Thereafter, using a sputtering device or other vacuum
vapor deposition device, a copper layer is formed on the dielectric
layer 43, and approximately 10 .mu.m of copper is added onto this
copper layer by electroless plating, etc., to form an upper
electrode 42 of substantially the same thickness as lower electrode
41. The dielectric characteristics of the high dielectric constant
sheet 340 that is thus obtained can be measured using an
impedance/gain phase analyzer (product name: 4194A, made by Hewlett
Packard Inc.) at conditions of a frequency of 1 kHz, a temperature
of 25.degree. C., and an OSC level of 1V. The specific dielectric
constant is approximately 1300. A metal layer of platinum or gold,
etc., besides copper, may be formed by the vapor deposition, and a
metal layer of nickel, tin, etc., besides copper, may be formed by
the electroless plating. Though the dielectric layer 43 is formed
of barium titanate here, the dielectric layer may be formed of any
one of strontium titanate (SrTiO.sub.3), tantalum oxide (TaO.sub.3,
Ta.sub.2O.sub.5), lead zirconate titanate (PZT), lead lanthanum
zirconate titanate (PLZT), lead niobium zirconate titanate (PNZT),
lead calcium zirconate titanate (PCZT), and lead strontium
zirconate titanate (PSZT) by using another sol-gel solution.
[0037] The following is another method for preparing high
dielectric constant sheet 340. First, a barium titanate powder
(HPBT Series, made by Fuji Titanium Industry Co., Ltd.) is
dispersed in a binder solution, prepared by mixing 5 weight parts
of polyvinyl alcohol, 50 weight parts of pure water, and 1 weight
part of dioctyl phthalate or dibutyl phthalate as a solvent-based
plasticizer with respect to the total weight of barium titanate
powder, and the dispersion is printed as a thin film of
approximately 5 to 7 .mu.m thickness onto lower electrode 41 formed
of nickel and having a thickness of 14 .mu.m by using a roll
coater, doctoring blade, .alpha. coater or other printing machine,
and is dried for 1 hour at 60.degree. C., 3 hours at 80.degree. C.,
1 hour at 100.degree. C., 1 hour at 120.degree. C., and 3 hours at
150.degree. C. to prepare an unsintered layer. Besides BaTiO.sub.3,
a paste containing one or two or more types of metal oxide,
selected from the group consisting of SrTiO.sub.3, TaO.sub.3,
Ta.sub.2O.sub.5, PZT, PLZT, PNZT, PCZT, and PSZT may be printed as
a thin film of 0.1 to 10 .mu.m thickness using a roll coater,
doctoring blade, or other printing machine and dried to an
unsintered layer. After the printing, the unsintered layer is
sintered at a temperature range of 600 to 950.degree. C. to form a
dielectric layer 43. Thereafter, a copper layer is formed on the
dielectric layer 43 using a sputtering device or other vacuum vapor
deposition device, and approximately 2 to 10 .mu.m of copper is
added onto this copper layer by electroless plating, etc., to from
an upper electrode 42 of substantially the same thickness as lower
electrode 41. Besides copper, a metal layer of platinum or gold,
etc., may be formed by the vapor deposition, and besides copper, a
metal layer of nickel, tin, etc., may be formed by the electroless
plating. A sputtering method using barium titanate as a target may
be instead employed.
[0038] Then, as shown in FIGS. 6B and 6C, the lower electrode 41 of
the high dielectric constant sheet 340 is partitioned into first
lower electrode 141 and second lower electrode 241 by a rectilinear
groove L1, and circular holes 141a and 241a are formed. FIG. 6C is
a sectional view taken on A-A of FIG. 6B. Here, a method for
partitioning the lower electrode 41 shall be described. First, a
resist is provided onto lower electrode 41 and exposed and
developed via a photomask to from a resist pattern that covers
regions besides rectilinear groove L1 that is to be formed. Then,
the portion of the lower electrode 41 that is not covered by the
resist is removed through treatment by etching solution to thereby
form a rectilinear groove L1, and thereafter, the resist is
removed. The circular holes 141a and 241a are likewise formed by a
photographic method (tenting method). As a result, the first lower
electrode 141 and the second lower electrode 241 is partitioned by
the rectilinear groove L1. Here, the groove width of rectilinear
groove L1 is set to a width by which the isolation of the adjacent
first lower electrode 141 and second lower electrode 142 with
respect to each other is maintained when the rectilinear groove L1
is filled with an insulating resin. In the etching step, a cupric
chloride etching solution may be used.
[0039] Next, as shown in FIG. 7A, the high dielectric constant
sheet 340 is adhered onto the core substrate 20, which is prepared
in advance, via a thermosetting resin film (ABF-45SH, made by
Ajinomoto Co., Inc.) under lamination conditions of a temperature
of 50 to 150.degree. C. and a pressure of 0.5 to 1.5 MPa, and cured
at 150.degree. C. to 170.degree. C. for 1 hour. The thermosetting
insulating film is thereby hardened and becomes an insulating layer
26. The board at this stage of the manufacturing method is shown in
FIG. 7B. The surfaces of first and second lower electrodes 141 and
241 of the high dielectric constant sheet 340 are preferably
roughened by for example, an inter-plate process (made by
Ebara-Udylite Co., Ltd.).
[0040] A commercially available etching resist (dry film) is then
adhered onto the wiring board in middle of preparation on which the
high dielectric constant sheet 340 has been laminated, and a
pattern is formed on the etching resist by exposure and development
that is normally performed to form a pattern on a multilayer
printed wiring board. After patterning, the portions on which the
etching resist is not formed are removed by etching and then the
etching resist is removed to form circular holes 351 and 352 (see
FIG. 8A). For example, a cupric chloride etching solution may be
used in the etching step. The circular holes 351 are formed at
positions corresponding to positions at which first lower via hole
conductor 145 and first upper via hole conductor 148 in FIG. 3 are
to be formed, and the circular holes 352 are formed at the
positions corresponding to positions at which second lower via hole
conductor 245 and second upper via hole conductor 248 in FIG. 3 are
to be formed. A UV laser is radiated onto positions at which the
circular holes 351 and 352 are formed, to form via holes 361 and
362 which pass through the high dielectric constant sheet 340 and
reach the conductor layers 22 positioned the below high dielectric
constant sheet 340 (see FIG. 8B). The via holes may be formed
instead by radiating the UV laser, etc., directly onto the upper
electrode 42 without providing circular holes 351 and 352.
[0041] Then, after applying an electroless plating catalyst onto
the surface of the wiring board (including the bottom surface and
peripheral walls of the respective circular holes 351 and 352 and
the respective via holes 361 and 362), the wiring board is immersed
in an aqueous electroless copper plating solution to form an
electroless copper plating film (not shown) of 0.6 to 3.0 .mu.m
thickness on the wiring board. An example of composition of the
aqueous electroless plating solution includes 0.03 mol/L of copper
sulfate, 0.200 mol/L of EDTA, 0.1 g/L of HCHO, 0.1 mol/L of NaOH,
100 mg/L of .alpha.-.alpha.'-bipyridyl, and 0.1 g/L of
polyethyleneglycol (PEG). After that, an electroless copper plating
film of 25 .mu.m thickness is formed on the electroless copper
plating film, and the respective circular holes 351 and 352 and the
respective via holes 361 and 362 are filled with copper. Thus,
portions of the copper filled in via holes 361, which is in contact
with the first lower electrode 141, becomes first lower via hole
conductor 145. And other portions of the copper filled in via holes
361, which is not in contact with the first lower electrode 141,
becomes first upper via hole conductor 148. Portions of the copper
filled in via holes 362, which is in contact with second lower
electrode 241, becomes second lower via hole conductor 245. And
portions of the copper filled in via holes 362, which is not in
contact with second lower electrode 241, becomes first upper via
hole conductor 248 (see FIG. 8C). An example of composition of the
aqueous electroless plating solution includes 200 g/L of sulfuric
acid, 80 g/L of copper sulfate, and 19.5 ml/L of additive (Cupracid
GL, made by Atotech Japan). The electroless copper plating can be
performed under the conditions that current density of 0.5 to 2
A/dm.sup.2, duration of 60 to 115 minutes, and temperature at
23.+-.2.degree. C.
[0042] An etching resist (dry film) is then adhered onto the
electroless copper plating film and is patterned (see FIG. 9A).
Portions at which the etching resist is not formed after patterning
are a portion corresponding to a rectilinear groove L2 that
partitions upper electrode 42 into first upper electrode 142 and
second upper electrode 242, a portion corresponding to a donut-like
clearance 142a for isolating first lower via hole conductor 145
from upper electrode 42, and a portion corresponding to a
donut-like clearance 242a for isolating second lower via hole
conductor 245 from upper electrode 42. The copper present at the
portions at which the etching resist is not formed is removed to
from rectilinear groove L2 and clearances 142a and 242a (see FIG.
9B). Thus, the upper electrode 42 is thereby partitioned into first
upper electrode 142 and second upper electrode 242, the first lower
via hole conductor 145 is isolated from the first upper electrode
142, and the second lower via hole conductor 245 is isolated from
the second upper electrode 242. The etching resist is thereafter
removed. By these steps, the first and second capacitors 140 and
240 are formed on the core substrate 20. Thereafter, buildup
portion 30 is laminated by the method described in paragraph
[0021]. In this process, electrodes that are to be the respective
pads 61 and 62 are formed on the uppermost layer of the buildup
portion 30, and a multilayer printed wiring board 10, illustrated
in FIG. 1 to FIG. 3, is thereby completed.
[0043] In the multilayer printed wiring board 10 described above,
because the first and second capacitors 140 and 240, which differ
in capacitance, are connected in parallel between the power line PL
and the ground line GL, the respective resonant frequencies differ
as shown in FIG. 5 and the impedance is restrained to a low level
across a broad frequency range. In addition, because the dielectric
layer 43 of substantially uniform thickness is used, the dielectric
constant layer 43 can be formed readily in the middle of forming
the multilayer wiring structure and the decoupling capacitors can
be formed readily in comparison to the case of using dielectric
layers that differ in thickness according to each capacitor.
[0044] In the dielectric layer 43, a single dielectric film is used
to prepare both of the first capacitors 140 and the second
capacitors 240. The trouble of partitioning an electric film is
eliminated and the manufacturing process is thus simplified in
comparison to the case of using dielectric layers that are
respectively partitioned for the lower electrodes and upper
electrodes of the respective capacitors 140 and 240.
[0045] Because the dielectric layer 43 uses a sintered ceramic
body, the dielectric constant .epsilon. can be adequately high. The
respective decoupling capacitors can thus be high in capacitance
and thereby the dielectric layer 43 is allowed to function as
charge supply sources for accommodating instantaneous lowering of
the power supply voltage as well as for reinforcing the signal
power supply.
[0046] The present invention is not restricted to the
above-described embodiment and can obviously be put into practice
in various modes within the technical scope of the invention.
[0047] In the above embodiment, the area of first lower electrode
141 and the area of first upper electrode 142 are made
substantially the same, and the two electrodes 141 and 142 are made
to oppose each other in the first capacitor 140. Similarly, the
area of second lower electrode 241 and the area of second upper
electrode 242 are made substantially the same, and the two
electrodes 241 and 242 are made to oppose each other in the second
capacitor 240. However, the area of first lower electrode 141 and
the area of first upper electrode 142 do not necessarily have to be
substantially the same dimension. For example, as shown in FIG. 10,
the area of first lower electrode 141 may be greater than the area
of first upper electrode 142, and the area of second lower
electrode 241 may be greater than the area of second upper
electrode 242. Here, the overlapping area between first lower
electrode 141 and first upper electrode 142 is made different from
the overlapping area between second lower electrode 241 and second
upper electrode 242. Because the first and second capacitors 140
and 240 differ in capacitance in this case as well, the same
effects as those of the above embodiment are achieved. Also, the
first capacitor 140 shown in FIG. 4 may be combined with the second
capacitor 240 shown in FIG. 10, or the first capacitor 140 shown in
FIG. 10 may be combined with the second capacitor 240 shown in FIG.
4. Furthermore, which of the upper and lower electrode areas is to
be larger may be determined arbitrarily. In all cases, the first
and second capacitors 140 and 240 are made to differ in
capacitance.
[0048] In the above embodiment, the first lower electrode 141 of
the first capacitor 140 and the second lower electrode 241 of the
second capacitor 240 are disposed apart from each other, and the
first upper electrode 142 of the first capacitor 140 and the second
upper electrode 242 of the second capacitor 240 are disposed apart
from each other. However, the electrodes do not necessarily have to
be disposed separately at both the upper and lower sides. For
example, as shown in FIG. 11, the lower electrode 41 may be
arranged as a single electrode plate and the first upper electrode
142 and the second upper electrode 242 may be disposed separately.
In this case, the overlapping area between first upper electrode
241 and lower electrode 41 is made to differ from the overlapping
area between second upper electrode 242 and lower electrode 41.
Because first and second capacitors 140 and 240 are made to
mutually differ in capacitance in this arrangement as well, the
same effects as those of the above embodiment are achieved.
Oppositely, the first lower electrode 141 and the second lower
electrode 241 may be disposed apart from each other, the upper
electrode may be arranged as a single electrode plate, and the
overlapping area between first lower electrode 141 and the upper
electrode may be made to differ from the overlapping area between
second lower electrode 241 and the upper electrode.
[0049] In the above embodiment, the first and second capacitors 140
and 240 are connected in parallel between the power line PL that
supplies power to the IC chip 70 and the ground line GL that
grounds the IC chip 70. In one modified arrangement, three or more
capacitors that differ in capacitance may be connected in parallel
between the power line PL and the ground line GL. When four
capacitors that differ in capacitance are connected in parallel,
for example, the low impedance range can be widened further as
shown in FIG. 12.
[0050] In the above embodiment, the high dielectric element sheet
340 is used to build the first and second capacitors 140 and 240 in
the multilayer printed wiring board 10. The first and second
capacitors 140 and 240 may be built in the multilayer printed
wiring board 10 by using a buildup method instead. For example, a
metal film is formed by plating, etc. on the insulating layer 26
and is exposed and developed to form a first lower electrode 141
and a second lower electrode 241, a dielectric layer of
substantially uniform thickness may then be laminated onto the
electrodes, and a metal film is formed by plating, etc. on the
dielectric layer and exposed and developed to form a first upper
electrode 142 and a second upper electrodes 242.
[0051] In the above embodiment, a single dielectric layer 43 is
used to prepare both the first capacitor 140 and the second
capacitor 240. However, the dielectric layer of first capacitor 120
and the dielectric layer of second capacitor 240 may be separately
disposed in parallel instead.
[0052] In the above embodiment, the cross-sectional shape of the BU
via hole conductor 34 is a cup-like shape (a so-called conformal
via). The BU via hole conductor 34 may be a so-called filled via,
with which a metal or conductive resin is filled into the cup.
[0053] In the above embodiment, the first and second lower
electrodes 141 and 241 of the first and second capacitors 140 and
240 are connected to the ground line GL, and the first and second
upper electrodes 142 and 242 are connected to the power line PL. In
one modified structure, the first and second lower electrodes 141
and 241 of the first and second capacitors 140 and 240 may be
connected to the power line PL, and the first and second upper
electrodes 142 and may be connected to the ground line GL.
* * * * *